نور مرئی به عنوان یک ابزار جدید برای حفظ کیفیت تازه کاهو پس از برداشت Visible light as a new tool to maintain fresh-cut lettuce post-harvest quality

1. Introduction Fresh-cut fruit and vegetables belong to the market segment that had shown the highest economical progression in the food industry history (Martín-Belloso and Soliva-fortuny, 2011) and has continued to grow up to 5–10% per year during the past decade. Salads represent 50% of this segment and tissue browning is the most common and serious disorder easily detected and rejected by consumers. Cut-edge browning results from an oxidation of the phenolic compounds present in the samples or neosynthesised after cutting mainly by polyphenoloxidase (PPO). The operations involved in the processing of fresh-cut lettuce such as cutting and drying cause tissue damage leading to a rapid quality deterioration and shelf-life reduction. Chemical treatments such as reducing agents or enzyme inhibitors have been studied to control the phenolic metabolism that leads to browning. However, the industry still needs a strategy to prevent browning without the use of chemical agents. Several physical methods have been proposed to extend the shelf-life such as modified atmosphere packaging (MAP) (Charles et al., 2005), heat treatments (Campos-Vargas et al., 2005; Djioua et al., 2009; Salman et al., 2008, 2007) or UV light application (Allende et al., 2006; Charles et al., 2013). Visible light exposure represents a novel approach, environmentalfriendly, that can be used to preserve the overall quality of fresh-produce. It is well known that in plants, darkness induces the expression of genes implicated in chlorophyll, protein and chloroplast degradation and an increase of the reactive species of oxygen (Wada and Ishida, 2009). However, in many cases, light is not controlled during postharvest storage and products are commercially stored in darkness, which induces senescence and accelerates this process significantly. Light exposure can retard tissue browning of fresh-cut romaine lettuces (Zhan et al., 2012), fresh-cut celery (Zhan et al., 2013c) and delayed the yellowing of broccoli (Büchert et al., 2011). Light has also a positive effect on nutritional quality. Continuous light (around 35 μmol −2 s −1 ) maintained soluble sugars and ascorbic acid in fresh-cut romaine lettuce (Zhan et al., 2013a). In spinach leaves, the endogenous pool of some vitamins (such as ascorbic acid, folate,.) showed higher values when leaves where stored under visible light than in the dark (Lester et al., 2010). Light could enhance ascorbic acid synthesis due to the increase of the photosynthetic capacity that induce the availability of soluble carbohydrates, especially glucose, enabling them to contribute to the control of the ascorbic acid pool size (Toledo et al., 2003).